Process for the preservation of naturally occurring natural rubber latex and product thereof



' teria and enzymes.

United States Patent PROCESS FOR THE PRESERVATION OF NAT- URALLY OCCURRING NATURAL RUBBER LA- TEX AND PRODUCT THEREOF Walter T. L. Ten Broeck, Jr., Serbalawan, Indonesia, assignor to The Goodyear Tire & Rubber Company, Akron, Ohio, a corporation of Ohio N0 Drawing. Application October 12, 1956 Serial No. 615,459

8 Claims. (Cl. 260-815) This invention relates to the preservation and stabilization of natural rubber latex and is particularly concerned with the preservation and stabilization of the latex with a minimum amount of preserving and stabilizing agents.

Latex as obtained from the rubber tree is a complex dispersion of low stability consisting of solids dispersed in an aqueous medium in the relationship of about 35% solids to 65% liquid. Generally about of the solids are non-rubber solids, which include mineral salts, resins, sugars and proteins. Bacterial action breaks down carbohydrates to form acids. The protein is generally considered to surround the rubber globules and to undergo enzymatic putrefaction on standing. This tends to depress the pH of the latex until it becomes acid, at which point the rubber solids coagulate. It is therefore necessary to add preservatives to natural rubber latex in order to re press the activity of bacteria and enzymes and to maintain the latex in an alkaline condition during storage and/or shipment.

It is customary to add a preservative to freshly gathered latex as it is gathered from the field in order to prevent premature coagulation and in order to stabilize the latex until it can be further treated. A number of chemical preserving agents have been used as preliminary preservatives, e.g., ammonia, formaldehyde, strong caustics, such as sodium hydroxide and potassium hydroxide, and various combinations of these and other chemicals. In addition, various other agents have been used, such as bacteriacides, e.g., arsenic trioxide, phenols, etc. The preliminary preserving agent which is customarily preferred is ammonia. After the natural latex reaches the processing station, it is further treated in order to stabilize the latex and prevent premature coagulation during transport and processing.

These various preservatives have not been completely satisfactory. For example, formaldehyde-preserved latex tends to thicken with age and thus becomes unmanageable even though the latex does not completely coagulate. Also, formaldehyde-preserved latex displays a serious lack of mechanical stability. Ammonia must be added to latex in a substantial quantity in order to raise the pH and to buifer the latex sufiiciently to inhibit the activity of bac- The excess ammonia must be removed prior to processing of the latex. The combination of formaldehyde and ammonia is undesirable because they react together to form hexamethylene tetramine which inactivates both of them. The various bacteriacides are undesirable because most of them are toxic and cannot be used in many latex fabricated articles. Thus, present methods for preserving and stabilizing natural rubber latex are unsatisfactory for one reason or another.

The present invention overcomes many of the dim- 2,888,504 Patented May 26, 1959 '2 culties with present practices and provides a process by which latex can be preserved for long periods of time with good mechanical stability and without the introduction of objectional or undesirable amounts of ammonia and/or preservatives.

It is therefore a general object of this invention to provide an improved process for preserving field latex.

It is a more specific object of this invention to provide an improved process for preserving latex at low ammonia content wherein latex is preliminarily preserved, followed by desludging to remove impurities and then concentrated, after which the latex is stabilized and preserved for storage and/ or shipment.

It is a further object of this invention to provide a latex having new and improved characteristics.

These and other objects will be apparent as the description proceeds.

In the practice of this invention, natural rubber latex is collected from the rubber trees in the presence of an initial preservative, as desired, collected at a field station, preliminarily treated with additional preservative and thereafter processed into preserved and stabilized latex for storage and/ or shipment. This invention is concerned with a low titer desludged uncoagulated natural rubber latex concentrated to a total solids content of at least by Weight containing, as a preservative and stabilizer, ammonia in a quantity insuflicient by itself to preserve and stabilize the latex and an auxiliary preservative.

After the latex has been collected at the field station, small controlled amounts of additional ammonia are customarily added to the latex, e.g., 0.1 to 0.3% by weight, based on the total weight of field latex. Small amounts of other known preservatives, such as formaldehyde or other auxiliary preservatives, and/or bacteriacides, may be added if desired. After preliminary preservation, the latex is desludged before further treatment.

Customarily, desludging is accomplished by means of centrifugal separators or vats having suitably placed outlets for removal of the latex after the sludge has settled to the bottom, although any desludging method can be used in the practice of the invention. Various methods for desludging latex are described in Latex Preservation, Concentration and Shipment by I. H. Pidford, The Rubber Research Institute of Malaya, 19 47, Kuala Lumpur.

Before creaming, desludging may be effected by means of centrifugal clarifiers or by placing the preliminarily preserved latex in large vats and allowing it to stand for a period of 12 to 24 hours for the sludge to settle. The sedimentated latex is then separated from the sludge, treated with creaming agent and allowed to stand undisturbed for a period of 20-48 hours at which time the upper cream layer will have attained a total solids content of 45-60% by weight. Thereafter the serum is removed and the preliminary cream remaining is treated with an auxiliary preservative together with additional ammonia as may be desired. The preliminary cream, now fully preserved, is allowed to stand for final creaming for a sufficient length of time to reach the desired high total solids content, preferably of 65-70%. The serum is drained away and the remaining cream blended until uniform.

Centrifugal concentration is efiected by passing the normal latex through a centrifuge machine. The latex is recovered as a rubber rich (cream) portion of normally 62-65% total solids content and a rubber poor (serum) portion of 5-15% total solids content. The sludge, havaesaaoa ing a specific gravity greater than that of the serum and the cream, remains in the centrifuge bowl.

Although the desludging and concentration are normally conducted simultaneously, they may be handled separately, if desired, in both the customary centrifuging and creaming processes. The latex is always concentrated to at least 60% by weight of rubber solids and is usually concentrated to about 62% by weight of total rubber solids by centrifuging and 66-70% by creaming. Desludging and concentration are preferably accomplished prior to the final preservation by means of any additional ammonia needed and the auxiliary preservative used. This is desirable because considerable loss of the soluble preserving agents would result from the removal of serum. Also, a. number of elements in the sludge, such as phosphates and polyvalent metal ions, might interfere with the activity of the preserving agents.

After desludging and concentration, the ammonia content is increased to about 0.1 to 1.0% by weight, based on the weight of the water in the latex, although about 0.5 to 0.8% by weight is preferred. The amount of ammonia added after desludging and concentration will depend upon the amount of residual ammonia remaining from the preliminary treatment. In order to insure alkalinity during storage and/or shipment, the pH of the latex should be adjusted to at least 8.5 to 10.5, although it may initially be as high as 11.5. This amount of ammonia is normally insufficient to preserve the latex, but when combined with the auxiliary preservatives of this invention, it is adequate. In this manner, a desirable low ammonia latex is prepared.

In combination with the ammonia, an auxiliary preservative, such as the preservatives of this invention, is necessary if the latex is to be preserved while the alkalinity is maintained at the low titer required in the practice of this invention. These chemicals serve as auxiliary preserving agents when added to the latex in controlled amounts along with ammonia, which is present by itself in an amount insufficient to preserve the latex. About 0.1 to 1.0% by weight, preferably about 0.250.65% by weight, based on the water content of the latex, when added with ammonia in concentrations of 0.1 to 1.0%, based on the water content of the latex, is sufficient to preserve the latex against premature coagulation. This is substantially equivalent to about 0.04 to 0.40% by weight when based on the total weight of concentrated latex.

The auxiliary preservatives which are useful in the practice of this invention are sulfur containing compounds which are compatible with and generally soluble in the latex or in the rubber hydrocarbons. These sulfur bearing compounds are (1) the Z-thio-thiazyl compounds conforming to the following structural formula:

wherein the Rs are selected from the group consisting of hydrogen, alkyl radicals containing from 1 to 9 carbon atoms, benzyl radicals, hydrocarbon substituted aryl radicals wherein the hydrocarbon substituents are straight chain aliphatic hydrocarbons having from 1 to 9 carbon atoms, carboxyl radicals, halogen radicals, cycloaliphatic rings formed by the joining together of the pair of Rs on the double bond carbons and arylene rings formed by the joining together of the pair of Rs on the double bond carbons; wherein R is selected from the group consisting of hydrogen, a metal selected from the group consisting of alkali metals and alkali earth metals, an ester forming organic radical, a thiocarbamyl radical and a radical conforming to the radical contained within the brackets of the structural formula; and wherein at least one R is always selected from the radicals other than hydrogen and (2) the thiocarbamyl-thin compounds conforming to the following structural formula:

wherein the Rs are selected from the group consisting of hydrogen, alkyl radicals containing from 1 to 9 carbon atoms, benzyl radicals and hydrocarbon substituted aryl radicals wherein the hydrocarbon substituents are straight chain aliphatic hydrocarbons having from 1 to 9 carbon atoms and cycloaliphatic rings formed by the joining together of the pair of Rs on the nitrogen atom; and wherein R is selected from the group consisting of hydrogen, an alkali metal, an alkali earth metal, a thiocarbamyl radical, an ester forming organic radical and a radical conforming to the radical contained within the brackets of the structural formula.

Examples of the 2-thio-thiazyl compounds which are useful in the practice of this invention are 2-mercapto thiazole; Z-mercaptotbiazoline; the aromatic mercapto thiazoles such as mercapto benzothiazole, mercapto naphthylthiazole, mercapto nitro-substituted benzothiazole, mercapto halogen (chloro, bromo and iodo) substituted benzothiazole, mercapto alkyl (l-9 carbon atoms) substituted benzothiazole; dinitrophenyl-Z-mercapto benzothiazole; phenyl carboxyl-Z-mercapto benzothiazole; benzyl-Z-mercapto benzothiazole, etc.; the alkali metal salts of the above compounds such as the sodium, potassium and lithium salts; the alkali earth metal salts of the above compounds such as the calcium, strontium and barium salts; the corresponding disulfide compounds and other compounds which conform to the structural formula.

Examples of the thiocarbamyl-thio compounds which are useful in the practice of this invention are the aliphatic thiuram sulfides such as tetraalkyl (1-9 carbon atoms) thiuram disulfides and the corresponding monosulfides; the cyclic thiuram disulfides prepared from piperidine, morpholine, pyrrolidine, etc. and the corresponding monosulfides; the alkali metal salts of the above compounds such as the sodium, potassium and lithium salts; the alkali earth salts of the above compound such as the calcium, strontium and barium salts; the acid esters of dialkyl (1-9 carbon atoms) thio-carbamyl compounds such as dimethyl thiocarbamyl mercapto acetic acid; the dithiocarbamates such as dithiocarbamates containing aliphatic radicals, cycloaliphatic radicals, aralkyl radicals, cycloaliphatic rings, etc.; dinitrophenyl dithiocarbamate, the dinitrophenyl alkyl (1-9 carbon atoms) dithiocarbamates; the alkali metal salts such as the sodium, potassium and lithium salts; the alkali earth salts such as the calcium, strontium and barium salts and other dithiocarbamyl compounds which conform to the structural formula.

If desired, various anionic and nonionic surface active agents may be added to the latex to increase the mechanical stability properties, because they do not afiect the preserving properties of the preservatives. Many useful anionic and nonionic surface active agents are contained in Synthetic Detergents and Emulsifiers-1955, by John W. McCutcheon, MacNair-Dorland Company,

generally be classified as soaps of fatty acids, metallic salts of fatty acid soaps, esters of fatty acids, sulfonated oils, phosphatides, fatty amides, glycolic ethers, high molecular Weight esters, terpene fatty acid salts, etc. More specifically, some of the preferred surface active agents are dialkyl esters of sulfosuccinic acids and the corresponding metallic salts, soribtan fatty acid salts, alkyl aryl sulfonates and the corresponding metallic salts, glycollic salts of fatty acids, alkyl phenyl poly glycol ethers, alkyl aryl sulfonates, alkyl aryl polyether alco- Inc. These anionic and nonionic surface active agents can hols, metallic soaps, etc. If one or more of these surface active agents is desired, the amount should be at least 0.05% by weight, but not over 0.50% by weight, based on the total content of'the latex, preferably 0.10 to 0.20%.

Specific examples of the preferred stabilizing agents are ammonium oleate or myristate and the correspond ing sodium or potassium soaps. If desired, mixed soaps may be used, such as the sodium or potassium soaps of coconut oil or castor oil. The sodium salt of an alkyl aryl polyether sulfonate, or the sodium salt of alkyl aryl polyether sulfate may be used, as nonionic stabilizers. Also, the alkyl aryl polyether alcohols may be used.

In the following examples, which are not intended to be limitations on the invention, fresh latex was preliminarily treated at a field collection station with the usual low ammonia content of 0.3% based on the weight of the latex. Thereafter, the preliminarily preserved-latex was .concentrated and desludged by passing it through a centrifuge. The centrifuged latex, having a total solids content of approximately 62% by weight, was further ammo niated to an ammonia content of 0.27%, based on the weight of latex. The 0.27% ammonia, basedon the .Weight of concentrate, is equivalent to 0.71% to 0.75% ammonia, based on the water content of 62.0% to 64.0% total solids concentrate. To the 62% rubber solids latex containing 0.27% ammonia by Weight, 0.30% by weight, based on the weight of the latex, of the indicated preservatives was added. These various samples were tested periodically to determine the KOH number, the VFA number and the pH as measures of the condition of preservation.

The KOH value is a standard rubber test designated as ASTM D1076-54T and is designed to give the number of grams of 'KOH required to neutralize 100.grams of rubber solids latex. It is performed by adjusting the ammonia content of 50 grams of latex to 0.5% by weight, based on the water content, adding HCHO to form hexamethylene tetramine, diluting to 30% solids and adding the KOH solution to the neutral point. This test is used in the rubber industry as a standard to show the relative quality of latex. A Well preserved concentrated latex increases gradually in KOH number from approximately 0.35 at one days age to a maximum of 0.70 at six months age. The increase is caused by normal hydrolysis of fatty acid non-rubber compounds in latex. A poorly or inadequately preserved latex will increase in KOH numher at a much more rapid rate. Accordingly, a consideration of both the age and KOH number of a latex will indicate the relative quality of the latex.

The VFA (volatile fatty acid) number is a test which has been proposed for adoption by the ASTM (American Socity for Testing Materials) and which is described in The Journal of Rubber Research Institute of Malaya for February 1953. The test is conducted by taking a 50 gram sample of latex, adding 50 milliliters of 40% ammonium sulphate solution thereto while warming over a water bath. After coagulation, the serum is removed and filtered. Twenty-five milliliters of the filtered serum are 'added to a flask and the same is acidified with N sulfuric acid. A third of the acidified serum is distilled in a steam distillation apparatus until about 50 milliliters of distillate has been collected. The distillate is aerated with carbon dioxide free air and titrated with 0.01 N bariumhydroxide using brom-thymol blue as an indidicator. The VFA- number is calculated and expressed as grams KOH per 100 grams of latex solids. This test is useful for showing how well the latex is or has been preserved, i.e., the effectiveness of preservation.

A perfectly preserved and uncontaminated latex will have a VFA number of 0.01 to 0.03 as a maximum. Any increase in VFA number is generally attributed to bacterial activity resulting in end product formation of volatile fatty acids. A latex is consideredsatisfactory if any 6 increase in VFA number has. stopped at a value of approximately 0.10 without further increase as the latex ages.

EXAMPLE I Centrifuged latex at 0.27% ammonia content on total weight of latex Latex 'ISO, KOH VFA Sample No. Age, PerpH N o. N 0

Days cent Control-Regina 2% -fi'fl- 13:23 812i 8:813 42 10. 46 o. 55 o. 021 B: Control-Low Ammonl- 2 61.37 10.18 0.43 0.018 ation (0.75% NE; on water 28 9. 82 0. 88 0. 35 Cc0nte$t).NH t -42 9.80 1.04 0.37

: 0.75 a s on -we er ar ears-3Z artist} 2% 13133 gilt 313%? m nz D 6 T$ g g t 42 10.00 0.75 0.025

a 3 on we er f.i? 3. ll%f} 2% 01% 3t? 0 er p enzo 9 Weight oflatexx 42 10.00 0.62 0.033

The eflectiveness of the thiazyl compounds as auxiliary preservatives is shown by Example I. With regular ammoniation of 1.80% NH on the latex water content, Sample A, the KOHpnurnber increase was normal, and the VFA number remained substantially unchanged at about 0.02, indicating no signs of bacterial activity. The low'ammoniation control, Sample 13, with 0.75% ammonia on the latex water content was inadequately preserved in that at 42 days latex age, the KOH number had increased to 1.04 and the VFA number to 0.37. Samples C and D, with the same low ammonia content of 0.75% on the latex water content and containing 0.2% and 0.3% respectively of mercaptobenzothiazole, were preserved substantially equivalent to the high ammonia content control of Sample A, as shown by equivalent KOH numbers and no substantial increase in VFA numbers.

EXAMPLE H centrifuged latex at 0.27% ammonia content on; total weight of latex Latex TSC, KOH VFA. Sample No. Age, PerpH No No.

Days cent 2 62.07 10. 60 0.43 0.017 A: Control-Regular Am- 28 10. 52 0. 51 0. 019 mmatmn- 42 10. 4s 0. as 0. 021 B: Control-Low Ammoni- 2 61. 37 10. 18 0.43 0.018 ation (0.75% N H3 On water 28 9. 82 0. 8B 0. 35 content 42 9.80 1. 04 0.37 C: 0.75% NHs (on water content) 0.2% by weight 2 61. 38 l0. l8 0. 46 0.018 of mercaptobenzothiazole 28 10.00 0.63 0.024 illisulglde (on weight of 42 10.03 0.63 0.022 a ex As in Example I, the disulfide also proved to be very eflective as an auxiliary preservative. Apparently, all bacterial and enzymatic action was stopped by the end of 28 days as illustrated by the steady KOH and VFA values.

7 EXAMPLE m Centrifaged latex at 0.27% ammonia content on total weight of latex Latex TSC, KOH VFA Sample N 0. Age, PerpH N o. N 0.

Days cent '7 A: ControlRegular Am- 8:

moniatlon- Z2 I 01 s 0. 024 B: Control-Low Ammonia- 2 63. 43 10. 00 O. 56 0. 12 tion' (0.75% NH: on Water 28 9. 60 1.01 0. 43 content). 42 Too thick to test 0: 0.75% NHa (on water content)+0.1% by Weight of 2 63. 62 10. 0. 50 0. 023 tetrarnethyl thluram mon- 28 10. 00 0. 62 0. 028 osulfide (on weight of 42 9. 86 0 67 0. 024 B 0 TH t t a onwa ercon- 6 0 48 L023 tent)+0.2% by weight of 63 43 0 64 (L028 tetramethyl thluraru mon- 42 9 8O 0 67 0 024 EoSu7lgeN(EoIn oitlatex).

i 0 a 1.1 .5 0.023 tent)+0.3% by weight of 3 63 57 g [L028 tetramethyl thiurarn mon- 42 9 86 0 67 0 024 osulfide (011 wt. of latex).

This example illustrates that the thiuram sulfides are very good auxiliary preservatives. Although the low ammonia control was too thick to test at 42 days, the samples (C, D and E) containing the thiuram sulfide preservatives compared almost exactly with the regular ammonia control.

EXAMPLE IV centrifuged latex at 0.27% ammonia content on total weight of latex This example illustrates that the thiuram disulfides also exhibit very desirable preservative activity.

EXAMPLE v centrifuged latex at 0.27% ammonia content on total weight of latex Latex 'ISO, KOH VFA Sample No. Age, PerpH N o N 0.

Days cent A: cqmroemuer i 28 .1838. 18:88 8: 28 8: 882 momaton- 42 10. 4s 0. 5e 0. 024 B: Control-Low Ammonl- 2 63. 43 10.00 0. 56 0.12 tlon (0.75% NH; 011 water 28 0. 60 1. 01 0. 43 cont.) 7. 1H t 42 Too thick to test 0:0.75 r 3 onwa ercontent)+0.2% by weight of 14 $8 8-; gtetramethyl thiuram tet- 42 0'024 rasulfido (on wt. of latex).

This example illustrates that the tetrasulfides also exhibit very good preservative properties.

8 EXAMPLE v1 centrifuged latex at 0.27 ammonia content on total weight of latex Latex 'ISC, KOH VFA Sample N 0. Age, PerpH No No.

Days cent A: Control-Regular Ammoniation. 5 033 B: ControlLo\v Ammoni- 0. 56 0.124 ation (0.75% N11 on water 0. 88 0. 290

Ccont.) .7 NH 0. 94 0.315

: 0.75 o 3 (on water A content) +03% by weight of sodium dibutyl dithio- 54 041 earbamate (on wt. of latex).

D: 0.75% N11 (on water 0 49 0 018 content)+0.l9% by weight 57 031 of sodium dibutyl dithio- 42 95 57 028 carbamate (on wt. of latex).

This example further illustrates that the soluble dithiocarbamyl-thio compounds are very effective as auxiliary preservatives in combination with ammonia, samples C and D being fully equivalent to the regular ammonia control which contained 1.80% by weight of ammonia. Thus, the eificacy of the soluble sulfur bearing compounds of this invention as auxiliary preservatives is established.

Although ammonia is described as the preferred alkaline material for use with the new preservatives disclosed in this invention, any basic material compatible with latex may be used, c. g., sodium or potassium hydroxide or phosphate, mono, di or tri methyl, or ethyl amine or other organic bases such as morpholine, piperidine, tetra methyl or ethyl ammonium hydroxide, etc.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

I claim:

1. A naturally occuring desludged uncoagulated natural rubber latex concentrated to a total solids content of about 60% to about 70% by weight containing as a preservative and stabilizer ammonia in a quantity insuffic'ient to preserve and stabilize the latex, said quantity of ammonia being insufficient to preserve the latex during shipment and storage and being present in such quantity as to preclude further processing to remove the ammonia prior to use in rubber processing applications, and an auxiliary preservative selected from the group consisting of (1) the 2-thio-thiazyl compounds conforming to the following structural formula:

wherein the Rs are selected from the group consisting of hydrogen, alkyl radicals containing from 1 to 9 carbon atoms, benzyl radicals, hydrocarbon substituted aryl radicals wherein the hydrocarbon substituents are straight chain aliphatic hydrocarbons having from 1 to 9 carbon j atoms, carboxyl radicals, halogen radicals, cycloaliphatic rings formed by the joining together of the pair of Rs on the double bond carbons and arylene rings formed by the joining together of the pair of Rs on the double bond carbons; wherein R is selected from the group consisting of hydrogen, a metal selected from the group consisting of alkali metals and alkali earth metals, an ester forming organic radical, a thiocarbamyl radical and a radical conforming to the radical contained within the brackets of the structural formula; and wherein at least one R is always selected from the radicals other than forming to the following structural formula wherein the Rs are selected from the group consisting of hydrogen, alkyl radicals'containing from I to, 9 carbon atoms, benzyl radicals and hydrocarbon substituted aryl radicals wherein the hydrocarbon substituents are straight chain aliphatic hydrocarbons having from l to 9 carbon atoms and cycloaliphatic rings formed by the joining together of the pair of Rs on the nitrogen atom; and wherein R is selected from the group consisting of hydrogen, an alkali metal, an alkali earth metal, a thiocarbamyl radical, an ester forming organic radical and a radical conforming to the radical contained within the brackets of the structural formula.

2. The product according to claim 1 wherein ammonia is added in an amount of 0.1 to 1.0% by weight, based on the weight of water in the latex and wherein the preservative is added in a quantity of from 0.1 to 1.0% by weight, based on the weight of the latex.

3. The Product according to claim 1 wherein the auxiliary preservative is at least one of the Z-thio-thiazyl compounds conforming to the following structural forwherein the Rs are selected from the group consisting of hydrogen, alkyl radicals containing from 1 to 9 carbon atoms, benzyl radicals, hydrocarbon substituted aryl radicals wherein the hydrocarbon substituents are straight chain aliphatic hydrocarbons having from 1 to 9 carbon atoms, carboxyl radicals, halogen radicals, cycloaliphatic rings formed by the joining together of the pair of R's on the double bond carbons and arylene rings formed by the joining together of the pair of Rs on the double bond carbons; wherein R is selected from the group consisting of hydrogen, a metal selected from the group consisting of alkali metals and alkali earth metals, an ester forming organic radical, a thiocarbamyl radical and a radical conforming to the radical contained within the brackets of the structural formula; and wherein at least one R is always selected from the radicals other than hydrogen.

4. The product according to claim 1 wherein the auxiliary preservative is at least one of the thiocarbamyl-thio compounds conforming to the following structural forwherein the Rs are selected from the group consisting of hydrogen, alkyl radicals containing from 1 to 9 carbon atoms, benzyl radicals and hydrocarbon substituted aryl radicals wherein the hydrocarbon substituents are straight chain aliphatic hydrocarbons having from 1 to 9 carbon atoms and cycloaliphatic rings formed by the joining together of the pair of Rs on the nitrogen atom; and wherein R is selected from the group consisting of hydrogen, an alkali metal, an alkali earth metal, a thiocarbamyl radical, an ester forming organic radical and a radical conforming to the radical contained within the brackets of the structural formula.

5. The process of preparing a naturally occuring desludged uncoagulated natural rubber latex for storage and shipment comprising (1) passing fresh naturally occuring rubber latex through a desludging and concentrating apparatus in order to remove the sludge and concentrate the latex to a rubber solids content of about 60% to about 70% by weight, (2) adding ammonia in a quantity-"insufficient to preserve the latex alone, said quantity of ammonia being insuflicient to preserve the latex during shipment and storage and being present in such-quantity as to preclude further processing to remove the ammonia prior to use in rubber processing applications, and an auxiliary preservative selected from the group consisting of the Z-thio-thiazyl compounds conforming to the following structural formula wherein the Rs are selected from the group consisting of hydrogen, alkyl radicals containing from 1 to 9 carbon atoms, benzyl radicals, hydrocarbon substituted aryl radicals wherein the hydrocarbon substituents are straight chain aliphatic hydrocarbons having from 1 to 9 carbon atoms, carboxyl radicals, halogen radicals, cycloaliphatic rings formed by the joining together of the pair of Rs on the double bond carbons and arylene rings formed by the joining together of the pair of Rs on the double bond carbons; wherein R is selected from the group consisting of hydrogen, a metal selected from the group consisting of alkali metals and alkali earth metals, an ester forming organic radical, a thiocarbamyl radical and a radical conforming to the radical contained within the brackets of the structural formula; and wherein at least one R is always selected from the radicals other than hydrogen and the thiocarbamyl-thio compounds conforming to the following structural formula wherein the Rs are selected from the group consisting of hydrogen, alkyl radicals containing from 1 to 9 carbon atoms, benzyl radicals and hydrocarbon substituted aryl radicals wherein the hydrocarbon substituents are straight chain aliphatic hydrocarbons having from 1 to 9 carbon atoms and cycloaliphatic rings formed by the joining together of the pair of Rs on the nitrogen atom; and wherein R is selected from the group consisting of hydrogen, an alkali metal, an alkali earth metal, a thiocarbamyl radical, an ester forming organic radical and a radical conforming to the radical contained within the brackets of the structural formula.

6. The process of claim '5 wherein ammonia is added in an amount of 0.1 to 1.0% by weight, based on the weight of water in the latex and the auxiliary preservative is added in an amount of 0.1 to 1.0% by weight, based on the weight of the latex.

7. The process of claim 6 wherein the auxiliary preservative is at least one of the Z-thio-thiazyl compounds conforming to the following structural formula wherein the Rs are selected from the group consisting of hydrogen, alkyl radicals containing from 1 to 9 carbon atoms, benzyl radicals, hydrocarbon substituted aryl radicals wherein the hydrocarbon substituents are straight chain aliphatic hydrocarbons having from 1 to 9 carbon atoms, carboxyl radicals, halogen radicals, cycloaliphatic rings formed by the joining together of the pair of Rs on the double bond carbons and arylene rings formed by the joining together of the pair of Rs on the double bond carbons; wherein R is selected from the group consisting of hydrogen, a metal selected from the group consisting of alkali metals and alkali earth metals, an ester forming organic radical, a thiocarbamyl radical and a radical conforming to the radical contained within the brackets of the structural formula; and wherein at least till one R is always selected from the radicals other than hydrogen.

8. The process of claim 6 wherein the auxiliary preservative is at least one of the thiocabamyl-thio compounds conforming to the following structural formula wherein the Rs are selected from the group consisting of hydrogen, alkyl radicals containing from 1 to 9 carbon atoms, benzyl radicals and hydrocarbon substituted aryl radicals wherein the hydrocarbon substituents are straight chain aliphatic hydrocarbons having from 1 to 9 carbon References Cited in the file of this patent UNITED STATES PATENTS Anderson Sept. 12, 1939 Young Sept. 19, 1939 

1. A NATURALLY OCCURING DESLUDGED UNCOAGULATED NATURAL RUBBER LATEX CONCENTRATED TO A TOTAL SOLIDS CONTENT OF ABOUT 60% TO ABOUT 70% BY WEIGHT CONTAINING AS A PRESERVATIVE AND STABILIZER AMMONIA IN A QUANTITY INSUFFICIENT TO PRESERVE AND STABILIZE THE LATEX, SAID QUANTITY OF AMMONIA BEING INSUFFICIENT TO PRESERVE THE LATEX DURING SHIPMENT AND STORAGE AND BEING PRESENT IN SUCH QUANTITY AS TO PRECLUDE FURTHER PROCESSING TO REMOVE THE AMMONIA PRIOR TO USE IN RUBBER PROCESSING APPLICATIONS, AND AN AUZILIARY PRESERVATIVE SELECTED FROM THE GROUP CONSISTING OF (1) THE 2-THIO-THIAZYL COMPOUNDS CONFORMING THE FOLLOWING STRUCTURAL FORMULA: 